This article shows how to connect to Box.net via the Mac Finder, giving you desktop access to a free, mountable 1 Gig online storage account. In a nutshell:

1) Get a box.net account.
2) In the Mac Finder select the GO menu then choose Connect to Server (Or Command-K).
3) Put in the address: https://www.box.net/dav
4) When it prompts, put in your Box.net username as your name and your Box.net password in the password field.

That’s it, look on your desktop. There should be a new connection mounded on your hard drive called dav.

Here’s an article for connecting to Box.net under Windows XP.

The secret is a web protocol called WebDav, which both XP and Mac support, and Box.net now provides as one of their many ways to access your Box.net file storage.